1. Field
The present disclosure relates generally to inlets and, in particular, to an inlet for a precooler in an engine system of a vehicle. Still more particularly, the present disclosure relates to a method and apparatus for improving performance of the vehicle using an inlet having a swept leading edge.
2. Background
In a turbofan engine, air is drawn into a main inlet of the engine by a fan. The fan pressurizes the flow of air and the air flows from the fan in two portions. A first portion of the air flows through the core of the engine. A second portion of the air flows through a fan duct that surrounds the core of the engine.
In certain situations, air may be “bled” from the core of an engine of an aircraft to supply an environmental control system (ECS), an anti-icing system, some other type of system of the aircraft, or a combination thereof. The air bled from the core of the engine may be referred to as “bleed air.”
The environmental control system of an aircraft may supply air to various areas and systems within the aircraft such as, for example, the cabin of an aircraft. In some cases, the bleed air may be too hot for use in the cabin, in other lower temperature areas of the aircraft, or in other types of areas. Consequently, the bleed air may first need to be cooled before being sent to the environmental control system. A precooler may be used to cool the bleed air. A precooler is a device or system that uses, for example, a heat exchanger to cool the bleed air prior to the bleed air being sent to the environmental control system.
Currently available precoolers typically use air flowing through the fan duct around the core of the engine to cool the bleed air. For example, an inlet located inside the nacelle of the engine may be used to direct a portion of the air flowing from the fan of the engine to the precooler. A duct connects the inlet to the precooler. Air that enters the precooler is slowed down, or diffused, through the duct prior to being fed into the precooler. A heat exchanger in the precooler then uses the diffused air to cool the bleed air.
During certain flight conditions, the bleed air may not need to be cooled. For example, during a cruise phase of flight, the bleed air may not need to be cooled using air from the fan. Thus, fan air flow into the precooler may be reduced to a low-flow state or a no-flow state during these flight conditions. In a low-flow state, the flow of air into the precooler may be significantly reduced. In a no-flow state, air may be prevented from flowing into the precooler. A valve system may be used to control the flow of air into the precooler. For example, a valve located upstream of the precooler may be used to reduce air flow into the precooler to either a low-flow state or a no-flow state during a cruise phase of flight.
However, in a low-flow state or a no-flow state, the inlet may disrupt the flow of air through the fan duct of the engine more than desired. In particular, the total pressure of the air from the fan may vary radially outward from the center axis of the fan. As used herein, the total pressure of the air is the sum of the static pressure of the air and the dynamic pressure of the air.
The variance in total pressure may result in undesired spillage during the low-flow state or the no-flow state based on current configurations for inlets. For example, undesired spillage may occur when a portion of the air flowing through the fan duct enters the inlet and then flows back out into the fan duct due to the low-flow state or the no-flow state. In other words, the air flows back out through the inlet into the fan duct, which causes an undesired disruption in air flow through the fan duct. This disruption in air flow may decrease aerodynamic performance more than desired.
Due to limitations on how quickly flow can be slowed down, or diffused, the duct used to connect an inlet to a precooler may be longer than desired. In particular, a longer duct may require that the precooler be mounted further aft. However, with the increasing size of precoolers, mounting these precoolers as far aft as needed may be more difficult than desired due to space limitations and physical constraints inside the nacelle of the engine. For example, a pylon structure may be attached to the nacelle of an engine and used to attach the engine to the airframe or wing of an aircraft. The pylon structure may extend inside of the nacelle in a manner that decreases the space available for mounting precoolers. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.